An inverter is an electrical device enabling conversion of DC (direct current) power from a DC power source to AC (alternating current) power. Herein ‘inverter’ generally refers to an electronic device or circuitry that is able to convert direct current to alternating current. An example of the inverter is a semiconductor bridge implemented by means of controllable semiconductor switches, such as IGBTs (Insulated-gate Bipolar Transistor) or FETs (Field-Effect Transistor), which are controlled according to a modulation or control scheme used.
One example of an electric system comprising an inverter is a photovoltaic system, such as a photovoltaic power plant or generator, in which one or more photovoltaic panels supply DC power to the inverter which converts the DC power to AC power, which may further be supplied to various AC loads via an AC network, for example. Large photovoltaic power plants may comprise a plurality of parallel inverters each receiving DC power from an array of photovoltaic panels. The inverter used may be a single-stage inverter or a multi-stage inverter. A single-stage inverter comprises only a single power electronic stage between the input and the output of the inverter taking care of not only the DC to AC conversion but also the possible maximum power point tracking, MPPT, and/or boosting functionality. An example of a multi-stage inverter is a two-stage inverter comprising a DC to DC stage and a separate DC to AC stage, wherein the DC to AC stage may perform the DC to AC conversion and the DC to DC stage may perform the possible MPPT and/or boosting functionality.
Inverters for such photovoltaic or other applications may be dimensioned and produced according to certain voltage, power etc. ratings. This dimensioning of the inverter typically defines allowed operation points for the inverter. In practice, the inverter may comprise certain set operational parameter limits which define limits for allowed operating points of the inverter. Such predetermined limitations may be based on expected worst case operational conditions in order to guarantee a certain minimum estimated lifetime for the inverter, for instance.
A problem related to the above solution is that the operation of the inverter might be far from optimal e.g. in case the actual operational conditions deviate essentially from the operational conditions used as a basis for the dimensioning of the inverter.